1. Field of the Invention
The present invention relates to an air-to-fuel ratio control system for an internal combustion engine, wherein a closed feedback loop for controlling the mixture ratio is switched off to an open loop during specific engine conditions.
2. Description of the Prior Art
A closed loop feedback control system for internal combustion engines has been highly appreciated from the point that the air-to-fuel ratio of the mixture to be supplied to the engine can be controlled to the stoichiometric ratio at which exhaust emissions therefrom becomes tolerable. It is a well-known matter, on the other hand, that the engine requires the air-fuel mixture other than the stoichiometric mixture upon specific engine conditions such as idling and that the oxygen responsive sensor is inoperative under the low ambient temperature. The closed loop feedback control, for this reason, must be switched off under these conditions.